Electroplating control system



Feb. 5, 1952 M. L. SANDS ELECTROPLATING CONTROL SYSTEM Filed Aug. 17, 1948 Patented Feb. s, lesa ELECTROPLATIN G CONTROL SYSTEM Matthew L. Sands, Everett, Mass.,

assignor to the United/ States of America as represented by the United States Atomic Energy Commission Application August 17, 1948, Serial No. 44,789 2 Claims. (Cl. 2011-231) This invention relates to an improvement in electroplating apparatus. More specifically the invention concerns a control system for maintaining constant the potential between the cathode and the plating solution Ain a. plating cell.

Many electroplating ,operations require extreme constancy and accuracy of the cathodeto-solution potential. This potential may vary during ordinary operation of a plating cell. Such variations occur because of variations in such factors as the current density at either or both of the electrodes, the extent of polarization at the electrodes, and the ion concentration, purity, and temperature of the plating solution.

It is accordingly the principal object of this invention to provide an improved electroplating apparatus wherein the potential between the cathode and the plating solution is maintained constant despite changes in conditions which may occur during the plating operation.

For understanding ofv the invention, reference is made to the attached drawing. AIn the drawing, the single ligure is a schematic dia-gram of an embodiment of the electroplating apparatus of the invention.

As shown in the drawing the plating cell I comprises a conventional anode I2 and cathode I4 disposed in a plating solution I6. A source of direct voltage I 8 having a potential of, for example, 90 volts is connected in series with vacuum tube 24 acting as a variable resistance and the plating electrodes. In the connection between the positive terminal of the voltage source I8 and the anode I2 are a conventional switch 2li` for starting and stopping the plating operation, and an ammeter 22 for indication of the value of the plating current. A voltmeter 26 is connected between the electrodes of the plating cell I 0 to indicate the potential difference therebetween. It will be seen that except for the control tube 24 the system as thus far described constitutes conventional electroplating apparatus.

The plating solution I6 is connected by a salt bridge 30 to the reference cell 32. Preferably the reference cell 32 is a calomel cell, shown in conventionalized fashion in the drawing. For the purpose of this specification electrode 3| will be designated as the negative terminal. This negative terminal of the calomel cell 32 is connected to the input grid 34 of a direct voltage electronic amplifier comprising a balanced-pair input stage 36, a single-tube stage 38, and an output tube 24, the anode and cathode of which are connected between the positive terminal of the voltage Source I8 and the anode I2 of the plating cell ID,

2 as described above. Thus any diierence of potential between the cathode I4 of the plating cell and the negative terminal of the calomel cell 32 is impressed on the input of the amplifier 35.

The amplifier 35 need not be further described herein since the particular direct voltage ampli-l fier circuit illustrated in the drawing does not in itself constitute and since persons skilled in the art will readily design many appropriate amplifiers for the purposes herein described.

It will be seen that if at any time during operation of the plating cell the plating solution I6 should become less positive withrespect to the cathode I4, the input grid 34 will become negative. This signal will be amplied and will appear as a positive signal on control tube 24. The voltage applied between the anode I2 and the cathode I4 will thus be increased, and the potential of the plating solution I6 will tend to be restored to its former value. Likewise, in similar fashion, if the plating solution I6 should become more positive with respect to the cathode I4, the amplier control tube 24 would serve to reduce the potential between the electrodes of the plating cell I0 and thus again tend to restore the original potential between the cathode I4 and the plating solution I6. The system preferably includes means e. g. potentiometer 33 whereby adjustment of the potential between the cathode I4 and the plating solution I6 may be accomplished to any predetermined value. The system described is seen to possess the desirable feature that no current is drawn through the calomel cell. A voltmeter 42 measures the potential between the cathode I4 and the negative electrode of the calomel cell 32. The voltmeter 42 is preferably a vacuum tube voltmeter. A suitable complement of parts and values of components are as follows:

Tubes 36 and 38 Type 6Q7 Tube .24 Type 6AK5 Resistors:

II, I3, and I5 K-- 300 I'I, I9, and 23 meg 4 25 and 33 meg 1 29, 30, and 31 meg 3 4I K wirewound 50 43 ohm 200 Capacitors 45 and 41 mfd .01

Persons skilled in the art will readily devise a. large number of equivalents for the system above described, utilizing the teachings of the invention. It will be understood that the embodiment the invention herein claimed,v

the grid 4E! of the shown in the drawing and described above is merely illustrative.

What is claimed is:

l. An electroplating system for maintaining the potential between a plating solution and plating electrode substantially constant, comprising an electroplating cell including a container for an electrolyte, an anode electrode and a cathode electrode immersed in the electrolyte; a rst thermionic tube having at least a cathode, anode, and a grid; means electrically connecting the electroplating cell anode and cathode, a source of plating potential and the anode and cathode of the first thermionic tube in series; means for varying the resistance of the rst thermionic tube in a direction to remove variations in potential between the electroplating cell cathode and the l electrolyte comprising means for supplying a constant reference potential; a direct current electronic amplifier having at least a rst grid controlled thermionic tube and means electrically connecting the grid-cathode space serially with said reference potential supply means, said electrolyte, and said electroplating cell cathode; means coupling the output of the electronic amplier across the grid-cathode space of the said rst thermionic tube with that polarity which increases the resistance thereof upon an increase in potential between the electroplating cell electrolyte and cathode and decreases the resistance thereof upon a decrease in potential between the electroplating cell, electrolyte and cathode, whereby tendencies to variation of potential between the electroplating cell electrolyte and cathode are inhibited.

2. An electroplating system having the characteristic of substantially constant potential between the electrolyte and cathode comprising an electroplating cell having a container for an electrolyte and an anode and cathode, and a grid controlled thermionic tube; means electrically connecting in series the electroplating cell anode, cathode and electrolyte with a source of plating potential and the anode-cathode nterelectrode space of said thermionic tube, means for varying the resistance of said thermionc tube in a direction to remove variations from a selected magnitude of the plating current comprising a cascade amplifier having a balanced ampliiier stage and a voltage amplifier stage and reference potential supply means, said balanced amplifier comprising a rst and a second grid controlled vacuum tube, means electrically connecting the cathodes of the vacuum tubes together and to a common load resistor, means electrically connecting the gridi cathode interelectrode space of one of said balanced amplifier vacuum tubes in series with the reference potential supply means and with the electrolyte and cathode of the electroplating cell; selectable potential means connected in series with the grid-cathode interelectrode space of the other balanced amplifier vacuum tube to adjust the potential between the electroplating cell electrolyte and cathode to a selected magnitude; means electrically coupling the anode of the said other balanced amplier vacuum tubes to the input of the voltage amplier stage and means electrically coupling the output of the voltage amplifier stage to the grid of the grid controlled thermionic tube.

MATTHEW L. SANDS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITEDA STATES PATENTS OTHER REFERENCES Transactions of The Faraday Society, January 1942, pages 27 to 33.

Principles of Electron Tubes," Graw-Hill, 1941, page 156.

Reich, Mc- 

